Leaves are green, thin flattened lateral outgrowths of the stem. They are borne at the nodes of the stem. Leaves are the chief organs of photosynthesis. The green leaves of the plant are collectively called as foliage of the plant.
Parts of a Leaf The three main parts of a typical leaf are
1. Leaf base
Leaf base : The part of the leaf which is attached to the stem or a branch is called leaf base. In some plants the leaf has a swollen leaf base. It is known as pulvinus eg. The compound leaves of the family Fabaceae.
In monocots the leaf base is very broad and flat and it clasps a part of the node of the stem as in maize and in banana. It is called sheathing leaf base.
Stipules: In most of the dicotyledonous plants, the leaf-base bears two lateral appendages called the stipules. Leaves which have the stipules are called stipulate.
The leaves without stipules are called exstipulate. The main function of the stipule is to protect the leaf in the bud.
Petiole : Petiole connects the lamina with the stem or the branch. A leaf is said to be petiolate when it has a petiole. It is said to be sessile when the leaf does not have a petiole.
Leaf blade: It is also known as lamina. This is the most important, green part of the leaf which is mainly concerned with the manufacture of food. The lamina is traversed by the midrib from which arise numerous lateral veins and thin veinlets.
The concept that the flower is a modified or a metamorphosed shoot for the purpose of reproduction is an old one and the concept is gradually developed through the past and is accepted at the present by a majority of morphologists.
Linnaeus expressed this idea in his Philosophia Botanica (1751) by the phrase “vegetative metamorphosis”.
This concept that floral leaves were a modification of vegetative leaves was further elaborated by Caspar Wolff and Decandolle.
The ‘ foliar theory’ of the flower of the earlier botanists is held today by many though modified in one form or other by other botanists. That the flower is a modified shoot, is only a figurative expression, and implies that the floral leaves are vegetative leaves and transformed to do a different function of reproduction, in the place of the ordinary function of photosynthesis.
A cell is a structural and functional unit of all living organisms. It is microscopic and capable of independent existence. All living things are made up of cells.
The outward differences among the various biological forms may bewilder us. But underlying these differences is a powerful uniformity.
That is all biological systems are composed of same types of molecules and they all employ similar principles of organization at the cellular level. We shall see for example, that all living organisms employ the same genetic code and a similar machinery for protein synthesis.
Organisms contain organs, organs composed of tissues, tissues are made up of cells; and cells are formed of organelles and organelles are made up of molecules. However, in all living organisms, the cell is the functional unit.
All of biology revolves around the activity of the cell. Loewy and Siekevitz defined cell as a unit of an organism delimited by a plasma membrane in animal cells and cell wall and plasma membrane in plant cells. Thus cell forms the basic unit of life.
The science of plant biology is primarily the study of flowering plants or angiosperms. Flowering plants square measure out and away the foremost necessary cluster of plants within the world, providing the overwhelming majority of plant species (over 250 000 in all) and most of the biomass onto land, and that they square measure the premise for nearly all our food.
Historically, the science of plant biology, or botany, has enclosed all living organisms except animals, however it’s clear that there’s a serious division of life between cells with an easy level of organization, the prokaryotes, and people with far more advanced cells, the eukaryotes.
The prokaryotes embrace microorganism and bacteria-like organisms and can not be thought-about more during this book except in regard to plants, though some retain plant-like names, like touching on the gut ‘flora’ for the microorganism in class guts, and blue-green algae’ for the true bacteria. Among eukaryotes 3 main cellular king doms square measure recognized: animals, plants and fungi. there’s a fourth hetero geneous cluster of eukaryotes that square measure chiefly animate thing however with a number of cellular teams like slime molds and enormous alga.
A number of these have affinity with animals, some with plants, some with fungi and a few don’t have any obvious affinity. they’re sorted along, for convenience, as a kingdom, the protists, division Protista (or Protoctista).
There is no clear boundary between protists and plants, and authors disagree during which organisms they take into account during which kingdom. cellular chlorophyte and, to a lesser extent brown and alga, have several options in common with land plants and square measure the dominant chemical change organisms in shallow seas. Animate thing being teams kind the premise of the organic phenomenon within the deep ocean. Of these alga square measure chemical change, like plants, and share some characters. they’re thought-about during this book for comparison with alternative plants in Section P. alternative protists, animals and fungi won’t be thought-about more except in regard to plants. Plant teams apart from flowering plants, like mosses, ferns and conifers, disagree in varied ways in which.
To characterize the options that outline plants as totally different from alternative eukaryotes is sort of not possible since each feature has exceptions, however typically these excep tions square measure among plants that have lost the feature or square measure among the alga on the boundary between protists and plants.
*They’re chemical change and procure all their nutrients from inorganic sources, i.e. they’re plant and also the begin of a organic phenomenon. several protists, significantly among the being, also are chemical change. a number of plants derive all or a part of their nutrients from alternative organisms. however these square measure closely associated with alternative, chemical change, flowering plants.
* The chemical change pigment is chlorophyl, and altogether plants except some alga, there square measure 2 forms, a and b, contained among chloroplasts.
*The cells have a semipermeable membrane created preponderantly of the sugar cellulose, and a cavity additionally to the protoplasm.
*There’s an alternation of diploid and haploid generations. usually one in all these is way reduced and should not live severally.
Vegetative structure and physiology is analogous throughout the seed plants (flowering plants, conifers and a few smaller groups) and there square measure several simi larities with alternative tube-shaped structure plants furthermore, however the procreative structures disagree markedly.
Larger alga and bryophytes disagree additional essentially in vegetative and plant organ.
Like islands in a vast sea of space, most galaxies are millions of light-years apart. However, some galaxies are close enough to be pulled by gravity into clusters. Members of galaxy clusters can pull on each other so strongly that they collide.
STEPHAN’S QUINTET Stephan’s Quintet is a group of galaxies that appear to be smashing into each other. Four of them are about 280 million light-years away from Earth, but the fifth is closer to us. NGC 7318b is passing through the main group at nearly 200 million mph (320 million km/h). This creates a shock wave that causes the gas between the galaxies to heat up and give out X-rays (the light blue region in the middle).
Cluster collision The ultimate crashes occur when several clusters of galaxies collide. The biggest collision astronomers have seen so far is a pile-up of four clusters called MACS J0717. This filament (stream) of galaxies, gas, and dark matter is 13 million light-years long. It is moving into an area already packed with matter, causing repeated collisions. When the gas in two or more clusters collides, the hot gas slows down. Galaxies don’t slow down as much, so they end up moving ahead of the gas.
A distorted view Some galaxy clusters act as magnifying glasses in the sky. Their powerful gravity distorts the space around them. This means that light from more distant galaxies or quasars is bent on its way to us. We see multiple arcs and distorted images of the distant object, like a mirage in space.
Radiation is energy within the kind of waves or streams of particles. There area unit several varieties of radiation all around us. Once individuals hear the word radiation, they usually think about nuclear energy, atomic power and radiation, however radiation has several different forms. Sound and visual light weight area unit acquainted types of radiation: different varieties embody ultraviolet light that produces a suntan), actinic ray (a kind of heat energy), and radio and tv signals.
Isotopes An atom could be a variant of a selected matter. whereas all isotopes of a given component have constant variety of protons, every atom includes a totally different variety of neutrons.
For example, H has 3 isotopes (or variants):
*Hydrogen-1 (contains one nucleon and no neutrons)
*Hydrogen-2, that is termed Hydrogen atom (contains one nucleon and one neutron).
*Hydrogen-3, that is termed Hydrogen (contains one nucleon and 2 neutrons)
Radioisotopes Isotopes that don’t seem to be stable and emit radiation area unit referred to as radioisotopes. A isotope is associate in nursing atom of part that undergoes spontaneous decay and emits radiation because it decays. Throughout the decay method, it becomes less radioactive over time, eventually changing into stable.
There area unit 3 main sorts of radioactive decay: *Alpha decay: Radioactive decay happens once the atom ejects a particle from the nucleus, that consists of 2 neutrons and 2 protons. Once this happens, the number decreases by a pair of and also the mass decreases by four. Samples of alpha emitters embody atomic number 88, radon, metallic element and atomic number 90.
*Beta decay: In basic radioactive decay, a nucleon is become a nucleon associate in nursing an negatron is emitted from the nucleus. The number will increase by one, however the mass solely decreases slightly. samples of pure beta emitters embody strontium-90, carbon-14, hydrogen and sulphur-35.
*Gamma decay: Gamma decay takes place once there’s residual energy within the nucleus following alpha or radioactive decay, or once nucleon capture (a sort of nuclear reaction) in a very reactor. The residual energy is discharged as a gauge boson of nonparticulate radiation. Gamma decay typically doesn’t have an effect on the mass or number of a isotope. samples of gamma emitters embody iodin. cesium-137, cobalt-60, radium-226 and technetium-99m.
Cancer risk assessment: The ICRP has calculated the likelihood of fatal cancer by relying totally on the assessment of radiation effects by scientific bodies like UNSCEAR and BEIR. It then determined what it calls the “detriment” of radiation exposure. This includes:
A vacuum is a space that has less gaseous pressure than the standard atmospheric pressure at sea level on Earth. A partial vacuum can be easily created by simply pumping air out of a container. If the container is not sealed, though, the air will be replaced fairly quickly.
In everyday life, vacuums are used in light bulbs, cathode ray tubes, cleaning appliances, and to package, protect and preserve a range of foodstuffs. Creating a vacuum drove the piston mechanism in the Newcomen steam engine and was also used in the braking systems of trains. Household vacuum cleaners work by sucking in air, which creates a lower air pressure than that outside the device. To restore the partial vacuum the outside pressure forces air, and with it dirt/dust etc, into the appliance.
The purest vacuums can be found in outer space Between galaxies, the vacuum density drops to -0.001 atoms per cubic centimetre, while in the void between stars in the Milky Way, the vacuum is -0.1-1 atoms per cubic centimetre. This is in contrast to a vacuum cleaner that produces a vacuum of around 1019 molecules per cubic centimetre, though highly sophisticated extreme-high vacuum (also known as XHV) lab chambers have managed to achieve a vacuum of fewer than 1,000 molecules per cubic centimetre.
Whether man-made or natural, there is no such thing as a perfect vacuum. Even in a virtually complete vacuum, physicists have discovered the presence of quantum fluctuations and vacuum energy. See opposite for more on fire and sound work inside a vacuum.
Solar tsunamis are surges of material sent crashing across the Sun as the result of a solar flare being launched into space. They can travel at speeds up to 1.6 million km (1 million miles) per hour. These solar tsunamis are made of hot plasma and magnetic energy.
The first was observed by Gail Moreton in 1959, and since then several more studies have been conducted by the Solar and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) spacecraft, both of which orbit the Earth.
Solar tsunamis are formed when the Sun emits a coronal mass ejection (CME) – a massive burst of solar wind commonly associated with solar flares. Around the ejection point, a circular wave extends outwards in all directions and travels across the surface of the Sun at a super-fast rate. In February 2009, the two STEREO spacecraft watched as a billion-ton cloud of gas was hurled off the surface of the Sun from a CME.
The result of this ejection was a massive solar tsunami that towered 100,000km (60,000 miles) high and which sped across the star’s surface at about 900,000km (560,000 miles) per hour. It was estimated to contain the same energy as 2.4 million megatons of TNT.
Solar wind streams from the Sun at a blistering 400 kilometres (250 miles) per second. The intense heat of the corona – the outermost portion of the Sun’s atmosphere – energises particles to such a level that the Sun’s gravitational field can no longer hold on to them and they escape into space.
Solar wind strength varies, creating space weather capable of disrupting technology, like global positioning system (GPS) satellites.
The movement of solar wind has a characteristic pattern that resembles a rope wobbling up and down – technically known as an Alfvén wave (after Hannes Alfvén). These magnetic strings can be observed as the greenish light that appears during the polar auroras.
Until recently scientists have struggled to understand this unusual wave behaviour, but a new set of models – based on similar waves generated by polarised light – might enable us to understand, and even predict, future fluctuations in solar wind.